ACROSS
 7. (SPORTS TEAM)* = POSTMASTER <person in charge of communications>
 9. <appearance> LOOK = K after LOO
10. <kingdom no longer existing> MERCIA = MERCI + A
11. <Lord> GOODNESS = (DOGE'S SON)*
12. <coda> TAIL = "TALE"
14. TEETER outside TRAM = TETRAMETER <lines>
16. <British summer> TURING = T [-sec]URING
17. <analysed> PARSED = PD outside ARSE
20. A after (H inside TRAPDOOR*) = ARTHROPODA <spiders, etc.>
22. <hairstyle> AFRO = (.e)AF RO(y.)
23. CHARM A outside "I"S = CHARISMA <it>
25. DEE + PLY = DEEPLY <without being shallow>
27. A CHE = ACHE <pine>
28. <difficult> UNENVIABLE = UNVIABLE outside EN

DOWN
 1. <Roman god> JOVE = V inside JOE
 2. <particular person> STICKLER = S (L inside TICKER)
 3. ←OI NOT NANA'S← = SAN ANTONIO <Texas city>
 4. DR NO, D→B = BRNO <Czech city>
 5. <drop> PLUNGE = LUNG inside PE
 6. (SEE DOLLARS)* = LOSS-LEADER <undervalued item>
 8. TIG + H + ←ST← = TIGHTS <legwear>
13. AFTERS HOCK = AFTERSHOCK <cause of rumbling later?>
15. <believe> ADAM AND EVE = EVADED* outside A MAN
18. <astronaut> SPACEMAN = S (E inside PACMAN)
19. MOLE outside RA = MORALE <confidence>
21. <god> HERMES = HEROES, M←O
24. "SOLE" = SOUL <person>
26. LIL T = LILT <vocal quality>